1. Field of the Invention
The present invention relates generally to welding processes and more particularly to an automatic arc welding process utilizing a consumable nozzle.
2. Description of the Prior Art
Although many attempts have been proposed to improve welding efficiency and to automate the welding process utilized in welding the block joints of the outer skins of a ship's bottom within the ship building industry, such attempts have only attained partial success in meeting the demands arising from such field. In addition, one-side automatic welding according to the prior art suffers from disadvantages in that a welding operator need always control the welding machine during the welding operation, and consequently, the one-side welding still remains in the semi-automatic state. Furthermore, the one-side welding process necessarily uses a welding carriage such that some limitation is imposed upon welding positions due to the structural restrictions inherent in the travel of the carriage.
On the other hand, there has been disclosed in Japanese Pat. Publication No. 17256/1969 a welding process whereby a wire is fed in a direction parallel to the joint line, however, such process nevertheless presents various disadvantages which may be enumerated as follows:
1. The welding positions capable of being used are limited to the range over which the welding carriage can travel. This results in the necessity for the weld line to have a substantial length, and furthermore, other welding processes have to be used for the terminal portion of the weld, i.e., the portion of the weld line corresponding to the length of the carriage due to the failure of the carriage to provide an access for welding within such portion.
2. The nozzle and wire have to be maintained separate from the base materials to be welded and positioned within the weld groove during the travel of the carriage such that severe accuracy is required in connection with the dimensions of the weld groove.
3. The carriage requires the use of rails which must run parallel to the weld groove.
4. Due to the fact that the carriage is integral with the backing materials, the cross-sectional configuration of the weld groove is limited to the "I" type, and furthermore a stable and uniform bead does not often result due to the traveling carriage.
5. Since the forward flow of deposited metal may be prevented only by means of an arc being produced from the wire, such process is not suited for a welding application where a great amount of deposited metal is required, and furthermore a small amount of deposited metal is stained during one cycle of the welding operation.
6. The process further entails the requirement that the welding speed be coincident with the traveling speed of the carriage, thus, the welding conditions are limited by the accompanying complex adjustments of the machine, resulting in various difficulties in setting the welding conditions.
7. According to the nature of this process, a substantial length of welding wire is required to protrude from a nozzle. The length of the nozzle cannot be extended however due to the considerations of electrical conductivity, and accordingly the wire tends to be twisted or to float one way or another, thereby presenting additional difficulties in setting the target.
8. The welding speed is quite slow thereby resulting in poor welding efficiency.
9. The process is not suited to the use of a consumable nozzle nor is it possible to simultaneous weld joints as in two-side welding such as is used for an X-shaped weld groove.
Heretofore, many other welding processes have been in wide use in connection with a vertical joint. However, such attempts are all related to the manner in which deposited metal is formed when proceeding in a direction moving vertically upwardly such that there is no possibility of the deposited metal becoming located above a consumable nozzle and therefore presenting no problems. However, if such attempts were used for welding in a substantially horizontal direction, the flow of the deposited metal would be directed toward the consumable nozzle and thereby result in the premature melting of the consumable nozzle while interrupting the deposition of the deposited metal within the weld groove.
Furthermore, in conventional welding processes, the use of the consumable nozzle or welding wire having a circular cross section sometimes leads to the formation of an unmelted zone within a portion of the weld groove. This is because the position of the nozzle and wire are too far away from the surfaces of the weld groove and further because the highly thermally conductive backing material is too close to the weld groove between the base materials. Still further, the reason may be that the slag being formed will permeate the gap between the nozzle and the weld groove.